1. Field of the Invention
This invention relates to a porous carbon-carbon composite and a process for producing the same. More particularly, it relates to a porous carbon-carbon composite having a suitable porosity and a high mechanical strength, which is superior in heat resistance, chemical resistance, and abrasion resistance, etc. and a process for producing the same.
The carbon-carbon composite of the present invention is useful as filter element materials, catalyst carriers, electrodes for fuel batteries, bearing parts, dry cell parts, accumulator parts, etc.
2. Prior Art
It is known that a porous carbon-carbon composite can be obtained by effervescing impregnation of a liquid carbonizable material into either a high strength, high modulus carbon fiber reinforcement material which is being wound to a desired shape, or into a material of a structure having a high strength, high modulus carbon fiber as its principal material, e.g., woven fabrics, three-dimensional woven fabrics, non-woven fabrics, unidirectionally arranged sheets, or by cutting a reinforcement material of a high strength, high modulus carbon fiber in short length, mixing it with a liquid carbonizable material and causing it to foam, followed by, in either way, carbonization and, if necessary, graphitization, with the liquid carbonizable material being used as a precursor of matrix carbon.
The problem of this process is that it is difficult to uniformly arrange the reinforcement material and pores. Thus, there are parts where mechanical strength is markedly different in the composite. Also distribution of pores is apt to be localized. On this account, the shaped products often have weakness and it is necessary to handle the products as a fragile thing. Also, since the distribution and arrangement of pores tend to be non-uniform, the quality of the product as a filter element material or a material for retaining a certain liquid is not good.
In order to solve this problem, a reinforcement material fiber was cut in very short length or proportion of the content of a reinforcement fiber was made smaller in prior processes. However, there is a problem in such processes, that effectiveness of use of a reinforcement material is not sufficient. As an alternative solution, a method is proposed in which very fine glass hollow cubes are mixed. However, this leads to introduction of impurities into a composite after carbonization as well as reduction of electric properties and corrosion resistance. There is also a problem in this method that production of a continuous pore type porous composite is difficult.
As a process for producing porous carbon materials which is different from the above-mentioned process, there is disclosed in U.S. Pat. No. 3,829,327 a method in which a web of a carbon fiber is coated with pyrolytic carbon formed by CVD process. This method has an advantage of forming products superior in chemical and electrical properties, but there are problems that this method is costly and strength is notably reduced if a carbon material having a large porosity is made.
Also, in U.S. Pat. No. 3,991,169, a process wherein a higher alcohol is caused to adhere to a pitch fiber mat to help local melt-adhesion of a pitch fiber is disclosed. But this method has a problem that a product having a high mechanical strength is difficult.
Also, U.S. Pat. No. 3,960,601 discloses a fibrous web obtained by infusiblization and carbonization treatment of a pitch fiber web produced by blow-spinning. However, a porous carbon material produced by this method is essentially an aggregate of a fiber and pore size is small. If it is attempted to make porosity larger, there is a problem that its mechanical strength is reduced.
It is an object of the present invention to overcome a problem of difficulty in making the distribution of a reinforcement material and pores uniform at the time of shaping and carbonizing a porous carbon-carbon composite, which difficulty brings about great changes of strength in the composite and thereby results in weak parts in the composite, a problem that pores arrange in a certain manner and weak parts are formed in the composite, and a problem that handling of the composite material is difficult due to formation of such weak parts.
The above-mentioned object can be accomplished according to the process of the present invention.